Method of making storage tube targets and resulting article



Aug. 29, 1961 R. RIGOT ETAL METHOD GE MAKING sToRAGE TUBE TARGETs AND RESULTING ARTICLE FIG.1

INVENTORS ROGER RIGOT BYPQJLWJQM ATTORNEY Unite tate The present application is a continuation-in-part of applicants abandoned application Serial No. 587,343, tiled May 25, 1956, entitled Improvements in Storage Tube Targets.

The present invention relates to charge-controlled storage tubes, and more particularly to a new process of manufacture of targets for such storage tubes.

It is an object of the present invention to provide improved targets having a long maximum reading duration, i.e., -a long maximum retention time of signal charge storage after generation of the charge on the target.

It is knolwn that targets having a charge-storage characteristic are used in tubes such as the Graphecon tube for obtaining a visual display of transient phenomena, with a good retention time.

The production of targets by the known manufacturing processes, even under identical manufacturing conditions, generally does not consistently provide a uniform or constant retention time `from one target to the next, and the retention time is shorter than desired for some applications.

Therefore, further objects of this invention are to provide -a process for manufacturing storage tube targets having identical retention time characteristics and to achieve reproducible uniformity of such characteristics in successively manufactured tubes.

The process for manufacturing targets for chargecontroflled storage tubes, according to the present invention, includes the steps of: applying a thin continuous solid film of an organic substance, such as, for instance, collodion, or parlodion, having traces of at least one impurity capable of activating an insulating substance which will be mentioned hereinafter, on a very thin metal grid, which supports the whole target arrangement; applying a very thin metal iilm, such as aluminum, `for instance, by vacuum evaporation, to one of the faces of said film; applying a very thin film of insulating substance, such as zinc sulphide, magnesium iiuoride, silicon monoxide, on the other `face of said iilm; and destroying the film of organic material, while retaining its impurities in the target, for instance, by baking the coated grid. A different group of insulating substances which may be used for the insulating layer in a similarly processed target structure includes sodium-aluminum fluoride and the alkaline earth metal uorides, namely, calcium fluoride, barium iiuoride and strontium fluoride.

These impurities, such as Zinc naphthenate, magnesium, sulphur, zinc oxide and organic zinc salts soluble or miscible with the above-.mentioned organic substance, such as a zinc salt `derived from a fatty acid (i.e., one of the oleate and stearate types), et cetera, which are mixed with the collodion in the proportion of about not more than l to 10,000 by Weight, for instance, partially convert the insulating coating of the grid into a semiconductor coating, thus creating an intermediate region between the insulating coating and the metal coating, and it appears that it is this region which confers to the target obtained, according to the invention, remarkable properties insofar as reading characteristics are concerned. The metal film of the target structure -uses a metal that is transparent to electrons, is able to form a very thin arent continuous layer, may be deposited by vacuum evaporation, land maintains its continuity, i.e., is devoid of friability, when the target structure is subjected to elevated temperatures of the order of 400 C. during the manu* facturing steps referred to herein. The organic iilm such as collodion or parlodion, on which the insulating and metallic films are deposited, is selected because of the following characteristics: ability to form a continuous, very thin homogeneous solid layer, the ability to spread this layer upon a liquid surface and the :ability to be chemically decomposed or vaporized when'heated to a temperature less than that which damages the other parts of the tube or target structure, such chemical decomposition being effected by destructive distillation as described herein.

The aforementioned impurities are believed to act as donor of electrons and are capable of activating the insulating layer to obtain semi-conducting properties between the metal iilm and the insulating layer.

The target according to the invention, therefore, comprises an intermediate region of a semi-conducting nature between the metal coating and the insulating coating, which coatings have thus an imperfect contact between them.

The invention will be better understood from the description of the appended drawing illustrating an embodiment thereof, wherein:

FIGURE l is a cross-sectional view, on a greatly enlarged scale, of a target according to the invention;

FIGURE 2. diagrammatically shows the structure of the finished target.

FIGURE 1 shows a thin film of collodion l, of constant thickness, obtained, for instance, according to a known technique which consists in dropping into a water bath containing a tine mesh metallic grid 2, a drop of collodion, and lifting said grid to bring it into contact with the collodion lfilm formed on the water surface. The eollodion lm is thus placed o-n the grid, without being perfectly stretched lbetween the wires of the grid. Accordling to the invention, the collodion used contains activating impurities, for instance, traces of zinc naphthenate. An aluminum coating 3 is then applied, by any suitable means, for instance, by vacuumv evaporation, on the free face of the collodion lm and a zinc sulphide coating 4 on the collodion iilm -f-ace contacting grid 2.

The zinc sulphide coating 4- is honey-combed, as appears frorn FIGURE l. Coating 3 has, in the example shown, Va thickness of the order of 1/20 micron and coating 4 ya thickness of the order of 1/2 micron, the grid having 2() meshes per mm.; it is obvious that all the values mentioned are by -way of example only and in no wise limitative.

Baking is then effected, at a temperature, for instance, of 400 C., rduring several hours, so as to eliminate the collodion by destructive distillation, the impurities it contains remaining or being retained between the two coatings 3 yand 4.

FIGURE 2 dagrarmnatically shows the structure obtained by this method. It is to be noted that the intermediate Iilm 1 has, in fact, no vwell defined limits, and the relative thickness illustrated of the respective coatings are not to be compared, in any Way, with the real thicknesses thereof.

Due to the activation of the zinc sulphide by the impurities which were contained in the collodion, region l provides an imperfect contact of di-symmetrical conductivity between zones 3 and 4. It is believed that this imperfect contact, which is an essential feature of the target according to the invention, imparts to the target structure remarkable properties as compared to conventional targets.

The retention `factor is high, of the order of 20 to 30 seconds, and is uniform as between successively produced targets. Further, a wider acceleration voltage range, from 2,500 volts up to 12,000 volts, may be employed than is usually possible; this has the advantage that for any given value of beam current and given quality of definition the acceleration voltage may have an appreciably lower value than heretofore possible so that the electron velocity is accordingly lower, and the beam scanning coil structures may thus be of smaller physical size with accompanying idecrease in their structural bulk. A screen according to the invention has relatively good transparency to electrons, and exhibits a substantially improved signalto-noise ratio.

We claim:

1. A process for manufacturing storage tube targets comprising the steps of: coating one face of ya fine mesh metallic grid with a thin film of collodion mixed with a very slight proportion of activating impurity for activating an insulating material; coating one face of said collodion film with a thin metallic layer; coating the other face of said collodion film with a thin film of said insulating material; and baking the structure thus obtained at a temperature of the order of 400 C. to eliminate the collodion from the structure while .retaining said impurities.

2. A process as claimed in claim l, wherein said metallic layer is aluminum.

3. A process as claimed in claim l, wherein said insulating film is zinc sulphide.

4. A process as claimed in claim l, wherein said insulating film is magnesium liuoride.

5. A process .as claimed in claim 1, wherein said insulating film is silicon monoxide.

6. A process as claimed in claim l, wherein said impurities are a zinc naphthenate.

7. A process as claimed in claim l, wherein said insulating material is selected from the group consisting of zinc sulphide, magnesium fluoride, and silicon monoxide; and wherein said impurity is selected from the group consisting of magnesium, sulphur, zine oxide, a collodionsoluble organic zinc salt, and zinc naphthenate.

8. Aprocess as claimed in claim 7 wherein said metallic layer is aluminum.

9. A process as claimed in claim 1, wherein said insulating material is selected `from the group consisting of zinc sulphide, magnesium iiuoride, and silicon monoxide, and wherein said impurity is a zinc naphthenate.

l0. A process for manufacturing storage tube targets comprising the steps of coating one face of a fine mesh metallic grid with a thin lm of collodion and containing a trace not over about one ten-thousandth part by weight of impurity susceptible to activate a given insulating material and selected from the group consisting of magnesium, sulphur, Zinc oxide, and collodion-soluble organic zinc salt, and Zinc naphthenate, coating one face of said film with a thin metallic layer, coating the other face of said film with a thin film of said given insulating material which is selected from the group consisting of zinc sulphide, magnesium fluoride, and silicon monoxide, and subjecting said organic substance to destructive distillation by heat treatment while retaining said impurity within the target structure comprising said metallic layer and said film of insulating material.

11. A process as claimed in claim 10, wherein said metallic layer is aluminum.

l2. A process for manufacturing storage tube targets, comprising the steps of coating one face of a fine mesh metallic grid with a thin film of an organic substance selected from the group consisting of collodion and parlodion and containing a predetermined very slight proportion of activating impurities susceptible to activate a given insulating material and selected lfrom the group consisting of magnesium, sulphur, Zinc oxide, organic zinc salts soluble in said organic substance, and zinc naphthenate, coating one face of said film with a thin metallic layer, coating the other face of said film with a thin film of said insulating material selected from the group consisting of zinc sulphide, magnesium fiuoride, and silicon monoxide, and destroying said organic substance by heat treatment while retaining said impurities in the target structure comprising said metallic layer and said film of insulating material.

13. A process for manufacturing storage tube targets, comprising forming on a liquid surface a thin film of an organic material which contains a trace of an impurity selected from the group consisting of magnesium, sulphur, zinc oxide, an organic Zinc salt soluble in said organic material, and zinc naphthenate, moving a fine mesh metallic grid upwardly through said liquid to deposit said film upon a face `of said grid and provide a grid-supported thin film coating thereon upon withdrawal of said grid from said liquid, vacuum-depositing onto one face of said grid-supported film a thin electron-permeable metallic film, vacuum-depositing onto the other face of said gridsupported film a thin film ofan insulating material selected `from the group consisting of Zinc sulphide, magnesium fiuoride, and silicon monoxide, and heat treating the target structure thus obtained to effect destructive distillation of said organic substance while retaining said impurity in the target structure.

14. A process as claimed in claim 13, wherein said metallic film is aluminum.

l5. A process as claimed in claim 14, wherein said organic substance is collodion.

16. A process as claimed in claim l5, wherein said heat treatment is effected at a temperature of about 400 C.

17. A process for manufacturing storage tube targets comprising the steps of: coating one face of a fine mesh metallic grid with a thin solid film of an organic substance capable of being vaporized by heating at a temperature of the order at 400 C. and containing a very slight predetermined proportion of activating impurities for activating a `given insulating material to give it Senliconducting properties; coating one face of said film with a thin metallic layer; coating the other face of said film with a thin film of said insulating material; and baking the structure thus obtained at a temperature of the order of 400 C. to eliminate said organic substance from between the metallic layer and the insulating film while retaining said impurities in the structure.

18. A storage tube target, comprising a fine mesh metallic grid; a composite layer supported by said grid and made up from (a) material selected from the group consisting of zinc sulphide, magnesium fluoride, and silicon monoxide, and from (b) material remaining after destructive distillation treatment of an organic material containing trace amounts of at least one impurity selected from the group consisting of magnesium, sulphur, zinc oxide, an organic zinc salt soluble in said organic material, and zinc naphthenate; and an electron-permeable metallic film supported by said composite layer.

19. A storage tube target, comprising a fine mesh metallic grid; a composite layer supported by said grid and made up from two superimposed films individually consisting of (a) material selected from the group consisting of zinc sulphide, magnesium fiuoride, and silicon monoxide, and from (b) material remaining after in situ destructive distillation treatment of an organic material containign trace amounts of at least one impurity selected from the group consisting of magnesium, sulphur, zinc oxide, an organic zinc salt soluble in said organic material, and zinc naphthenate; and an electron-permeable aluminum film supported by said composite layer and placed thereon prior to said destructive distillation treatment.

20. A storage tube target according to claim 18 wherein said electron permeable metallic film is aluminum, intimately adherent to a surface of said composite layer.

21. A storage tube target, comprisingv a ne mesh metallic grid; a composite layer supported by said grid and made up from (a) a thin layer of material selected from the group consisting of zinc sulphide, magnesium fiuoride, and silicon monoxide", and from (b) material remaining after destructive distillation treatment of a thin layer on said first-mentioned thin layer of an organic material containing trace amounts of at least one impurity selected from the group consisting of magnesium, sulphur, zinc oxide, an organic zinc salt soluble in said organic material, and zinc naphthenate; and an electron-permeable metallic film supported by said composite layer.

22. A storage tube target according to claim 2l wherein said electron permeable metallic film is aluminum deposited on the organic-material-layer side of said composite layer prior to said destructive distillation treatment and adherent to said composite layer following said treatment.

23. A storage tube target, comprising a fine mesh metallic grid, a thin film of insulating material on said grid, a thin metallic layer on said thin film of insulating material and activating impurities between said insulating film and said metallic layer and activating said insulating material to give it semi-conducting properties and providing an imperfect contact between said film and layer and obtained by elimination of a thin solid film of an organic substance which contained said impurities in a predetermined slight proportion and was disposed between said insulating film and said layer.

24. A storage tube target comprising, a fine mesh metallic grid having an adherent thin film coating of a material of the electrical insulation type, and an electronpermeable metallic film adherent to a face of said material, a lamination of fractional micronic depth between said metallic film and the other face of said material, said lamination comprising some of said electrical insulation material and an impurity for making it electrically semiconductive.

25. A storage tube target comprising, a fine mesh metallic grid having an adherent thin film coating of a material selected from the group consisting of zinc sulphide, magnesium iiuoride, and silicon monoxide, and an electron-permeable metallic film adherent to a face of said material, a lamination of fractional micronic depth located between said metallic film` and the other face of said material being electrically semi-conductive by virtue of its formation by an impurity selected from the group consisting of magnesium, sulphur, zinc oxide, a soluble organic zinc salt, and zinc naphthenate.

26. A storage tube target according to claim 25, wherein said lamination is electrically semi-conductive by virtue of its creation with said impurity at an elevated temperature.

27. A storage tube target comprising, a fine mesh metallic grid having an adherent thin film coating of a material selected from the group consisting of zinc sulphide, magnesium fluoride, and silicon monoxide, an electron-permeable metallic film adherent to a face of said material, and a lamination of electrically semiconductive material located between said metallic film and the other face of said material and formed by destructive distillation of a collodion film containing a tra-ce of a material selected from the group consisting of magnesium, sulphur, Zinc oxide, a collodion-soluble organic zinc salt, and zinc naphthenate.

28. A Istorage tube target according to claim 27 wherein said lamination is formed by destructive distillation at an elevated temperature of a collodion film wherein said trace of a material is not over about one ten-thousandth art. p 29. A storage tube target comprising, a fine mesh metallic grid having a coating film of evaporation-deposit thinness and formed of a material selected from the group consisting of zinc sulphide, magnesium fluoride, and silicon monoxide, an aluminum film having an evaporationdeposit thinness permeable to electrons and being adherent to a surface of said coating lm,land an electrically semiconductive lamination of fractional micronic thickness interposed between said aluminum film and the other `surface of said coating film and formed by use of a material selected from the group consisting of magnesium, sulphur, zinc oxide, a soluble organic zinc salt, and zinc naphthenate.

30. A storage tube target according to claim 27, wherein said trace is about one ten-thousandth part by Weight of said collodion and wherein said electron permeable film is aluminum.

31. A storage tube target comprising, a fine mesh metallic grid, a thin fihn of insulating material on said grid, a thin electron permeable metallic layer on said thin film of insulating material, and at least one activating impurity between said insulating film and said metallic layer to provide between said film and layer electrical semiconductivity obtained by destructive distillation at elevated temperature of a thin solid film of an organic substance which contained said activating impurity in a predetermined slight proportion and which was disposed for, and readily eliminated by, destructive distillation between said insulating film and said layer.

32. A storage tube target comprising, a fine mesh metallic grid, a Zinc sulphide film of evaporation-deposit thiness on said grid, an electron-permeable film of aluminum on said z-inc sulphide film, and an electrically semiconductive laminar material between the exposed surfaces of said films obtained by destructive distillation at elevated temperature of a collodion film which contained zinc naphthenate in the proportions of not over one part zinc naphthenate to about ten thousand parts by weight of collodion.

33. A storage tube target, comprising on a support, a composite layer made up from a thin electron-permeable metallic film and a thin film of insulating material With a semi-conducting imperfect contact layer between said films comprising material obtained by destructive distillation upon heating of a thin solid film of an organic substance readily destroyed by destructive distillation and containing a slight trace of activating impurities disposed between said films.

34. A storage tube target comprising on a relatively rigid support a thin continuous film of metal capable of being deposited on a surface by evaporation, said metal film being transparent to electrons and retaining its continuity at elevated temperatures of the order of 400 C., a thin electrically insulating film of material capable of being activated to a state having semi-conducting properties by incorporation of' an impurity, and a layer of material including some of said impurity in said target providing a semi-conductive region between said films and obtained by destructive distillation of an organic material from a continuous solid film containing said organic material and a predetermined slight proportion of said impurity.

35. A process for manufacturing storage tube targets comprising the steps of: coating one face of a fine mesh metallic grid with a thin film of collodion, coating one face of said collodion film with a continuous thin electron-permeable metallic layer, coating the other face of said collodion film with a thin film of insulating material, and baking the structure thus obtained at a temperature of the order of 400 C. to eliminate the collodion from between said films by destructive distillation.

36. A process for manufacturing storage tube targets, comprising forming on a liquid surface a thin solid film of an organic material which is readily destroyed by destructive distillation and contains a trace of impurity for activating a given insulating material, transferring said film of organic material from the liquid surface to a fine mesh metallic grid, vacuum depositing onto one face of said grid supported film a thin electron permeable metallic film, vacuum depositing onto the other face of said grid supported film a thin film of said given insulating material, and heat treating the target structure thus obtained to effect destructive distillation of said organic material while retaining in a contacting region of said insulating and metallic films material including said impurity to provide imperfect contact with semi-conducting properties in the target structure.

37. A storage tube target, comprising on a support, a composite layer made up from a thin electron-permeable metallic film and a thin film of insulating material selected from the group consisting of sodium-aluminum fluoride and alkaline earth metal fluoride with a semi-conducting imperfect contact between said films comprising material obtained by eliminating by destructive distillation a thin film of an organic substance disposed between said films.

38. A storage tube target comprising on a relatively rigid support a thin continuous film of metal capable of being deposited on a surface by evaporation, said metal film being transparent to electrons and retaining its continuity at elevated temperatures of the order of 400 C., a thin electrically insulating film of material capable of being activated to a state having semi-conducting properties by incorporation of an impurity and selected from the group consisting of sodium-aluminum fluoride and alkaline earth metal fiuorides, and a layer of material including some of said impurity in said target providing a semi-conductive region between said films and obtained by destructive distillation of an organic material from a film containing said organic material and a predetermined slight proportion of said impurity.

39. A process for manufacturing storage tube targets comprising the steps of: coating one face of a fine mesh metallic grid with a thin film of collodion, coating one face of said collodion film with a continuous thin electron-permeable metallic layer, coating the other face of said collodion film with a thin film of insulating material selected from the group consisting of sodium-aluminum fiuoride and alkaline earth metal fluorides, and baking the structure thus obtained at a temperature of the order of 400 C. to eliminate the collodion from between said films by destructive distillation.

40. A process for manufacturing storage tube targets, comprising forming on a -liquid surface a thin film of an organic material which contains a trace of impurity for activating a given insulating material, transferring said film of organic material from the liquid surface to a fine mesh metallic grid, vacuum depositing onto one face of said grid supported film a thin electron permeable metallic film, vacuum depositing onto the other face of said grid supported film a thin film of said given insulat- -ing material selected from the group consisting of sodiumaluminum fluoride and alkaline earth metal fluoride, and heat treating the target structure thus obtained to effect destructive distillation of said organic substance while retaining in a contacting region of said insulating and metallic films material including said impurity to provide imperfect contact with semi-conducting properties in the target structure.

4l. A process for manufacturing storage tube targets, comprising the steps of coating one face of a fine mesh metallic grid with a thin film of an organic substance selected from the group consisting of collodion and parlodion and containing a predetermined very slight proportion of activating impurities susceptible to activate a given insulating material and selected from the group consisting of magnesium, sulphur, Zinc oxide, soluble organic zinc salts and zinc naphthenate, coating one face of said film with a thin metallic layer, coating the other face of said film with a thin film of said insulating material, and eliminating said organic substance by heat treatment while retaining said impurities between the metallic layer and the insulating film.

References Cited in the le of this patent UNITED STATES PATENTS 2,579,772 Wilder Dec. 25, 1951 

1. A PROCESS FOR MANUFACTURING STORAGE TUBE TARGETS COMPRISING THE STEPS OF: COATING ONE FACE OF A FINE MESH METALLIC GRID WITH A THIN FILM OF COLLODION MIXED WITH A VERY SLIGHT PROPORTION OF ACTIVATING IMPURITY FOR ACTIVATING AN INSULATING MATERIAL; COATING ONE FACE OF SAID COLLODION FILM WITH A THIN METALLIC LAYER; COATING THE OTHER FACE OF SAID COLLODION FILM WITH A THIN FILM OF SAID INSULATING MATERIAL; AND BAKING THE STRUCTURE THUS OBTAINED AT A TEMPERATURE OF THE ORDER OF 400* C. TO ELIMINATE THE COLLODION FROM THE STRUCTURE WHILE RETAINING SAID IMPURITIES. 